The M-16 Bouldering Brush by Metolius is THE ideal brush for cleaning nasty, grimy, chalked holds before you send. This brush was originally designed to clean the internals of an M-16 rifle, with one side of the brush has smaller bristles for those tiny spots you need to get into and the other side has a larger brush for those jugs and shelves. Super stiff bristles take chalk and grime right off and can also be used to clean the intricate parts of your cams.